《Spring源码深度解析》---第2章（容器的基本实现）

本文学习《Spring源码深度解析》（郝佳编著），实战笔记。

2.1容器的基本用法

首先笔者导入了spring-beans工程（导入源码方法点击我），在此工程下，结合书中的示例，如下创建文件，验证书中所写！

MyTestBean.java

/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.myBean;

/**
 * 
 * @author ccnu
 * @since 4.3
 */
public class MyTestBean {

	private String testStr = "testStr";

	public String getTestStr() {
		return testStr;
	}

	public void setTestStr(String testStr) {
		this.testStr = testStr;
	}

}

MyBeanFactoryTest.xml

MyBeanFactoryTest.java

/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.myTest;

import org.junit.Test;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.myBean.MyTestBean;

import static org.junit.Assert.*;

/**
 * 
 * @author ccnu
 * @since 4.3
 */
@SuppressWarnings("deprecation")
public class MyBeanFactoryTest {

	@Test
	public void testSimpleLoad() {
		BeanFactory bf = new XmlBeanFactory(
				new ClassPathResource("MyBeanFactoryTest.xml"));
		MyTestBean myTestBean = (MyTestBean) bf.getBean("myTestBean");
		assertEquals("testStr", myTestBean.getTestStr());
	}
}

2.4.2核心类介绍

DefaultListableBeanFactory

org.springframework.beans.factory.support.DefaultListableBeanFactory
右键-Open Type Hierarchy，如下：


据此可以用插件或者直接用power designer等工具画出UML类图。为了节省时间，笔者直接用了百度图片（图片来源链接）：

2.5容器的基础XmlBeanFactory

深入分析下面代码的实现：

BeanFactory bf = new XmlBeanFactory(
				new ClassPathResource("MyBeanFactoryTest.xml"));

XmlBeanFactory的初始化时序图如下（图片链接地址）：

2.5.1配置文件封装

Resource.java

package org.springframework.core.io;

public interface Resource extends InputStreamSource {

	boolean exists();
	boolean isReadable();
	boolean isOpen();
	URL getURL() throws IOException;
	URI getURI() throws IOException;
	File getFile() throws IOException;
	long contentLength() throws IOException;
	long lastModified() throws IOException;
	Resource createRelative(String relativePath) throws IOException;
	String getFilename();
	String getDescription();

}

InputStreamSource .java

package org.springframework.core.io;

public interface InputStreamSource {

	InputStream getInputStream() throws IOException;
}

ClassPathResource类实现了Resource接口，实际例子中用到的就是一个构造方法：

ClassPathResource.java实现的getInputStream方法：

FileSystemResource.java实现的getInputStream方法：

其他类似。

package org.springframework.beans.factory.xml;

@Deprecated
@SuppressWarnings({"serial", "all"})
public class XmlBeanFactory extends DefaultListableBeanFactory {

	private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);

	public XmlBeanFactory(Resource resource) throws BeansException {
		this(resource, null);
	}

	public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
		super(parentBeanFactory);
		this.reader.loadBeanDefinitions(resource);
	}

}

/**
	 * Create a new AbstractAutowireCapableBeanFactory.
	 */
	public AbstractAutowireCapableBeanFactory() {
		super();
		ignoreDependencyInterface(BeanNameAware.class);
		ignoreDependencyInterface(BeanFactoryAware.class);
		ignoreDependencyInterface(BeanClassLoaderAware.class);
	}

2.5.2

下面图片来源链接

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			Document doc = doLoadDocument(inputSource, resource);
			return registerBeanDefinitions(doc, resource);
		}
		catch (BeanDefinitionStoreException ex) {
			throw ex;
		}
		catch (SAXParseException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
		}
		catch (SAXException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"XML document from " + resource + " is invalid", ex);
		}
		catch (ParserConfigurationException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Parser configuration exception parsing XML from " + resource, ex);
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"IOException parsing XML document from " + resource, ex);
		}
		catch (Throwable ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Unexpected exception parsing XML document from " + resource, ex);
		}
	}

跟踪到上面的代码，上面这个方法有两行是核心：

Document doc = doLoadDocument(inputSource, resource); //加载XML文件，获取Document
return registerBeanDefinitions(doc, resource); //根据返回的Document，注册Bean信息

追踪doLoadDocument方法如下：

protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
		return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
				getValidationModeForResource(resource), isNamespaceAware());
	}

最终参数中的getValidationModeForResource方法：

protected int getValidationModeForResource(Resource resource) {
		int validationModeToUse = getValidationMode();
		
		// 人为指定了，就用人为指定的约束
		if (validationModeToUse != VALIDATION_AUTO) {
			return validationModeToUse;
		}
		int detectedMode = detectValidationMode(resource);//未指定，就调这个方法
		if (detectedMode != VALIDATION_AUTO) {
			return detectedMode;
		}
		// Hmm, we didn't get a clear indication... Let's assume XSD,
		// since apparently no DTD declaration has been found up until
		// detection stopped (before finding the document's root tag).
		return VALIDATION_XSD;
	}

上面这个方法是获取对XML文件的约束模式（XSD、DTD）。下面这个方法就是检查到底用了DTD约束，还是用了XSD约束！方法就是一行一行扫描XML文档，如果包含DOCTYPE就表明是DTD约束，否则就认为是XSD约束。

public int detectValidationMode(InputStream inputStream) throws IOException {
		// Peek into the file to look for DOCTYPE.
		BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
		try {
			boolean isDtdValidated = false;
			String content;
			while ((content = reader.readLine()) != null) {
				content = consumeCommentTokens(content);
				if (this.inComment || !StringUtils.hasText(content)) {
					continue;
				}
				if (hasDoctype(content)) {//如果包含DOCTYPE就是DTD约束
					isDtdValidated = true;
					break;
				}
				if (hasOpeningTag(content)) {
					// End of meaningful data...
					break;
				}
			}
			return (isDtdValidated ? VALIDATION_DTD : VALIDATION_XSD);
		}
		catch (CharConversionException ex) {
			// Choked on some character encoding...
			// Leave the decision up to the caller.
			return VALIDATION_AUTO;
		}
		finally {
			reader.close();
		}
	}

关于XML文件的验证（约束）模式，就两种，分别是XSD和DTD，笔者观察到了一个明显的区别就是用DTD约束的XML会有DOCTYPE说明，而XSD约束的XML没有。

DTD约束的XML头：

XSD约束的XML头：

2.7获取Document

追踪代码到registerBeanDefinitions方法：

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getRegistry().getBeanDefinitionCount();
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

继续追踪到registerBeanDefinitions方法：

@Override
	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		Element root = doc.getDocumentElement();
		doRegisterBeanDefinitions(root);
	}

继续追踪到doRegisterBeanDefinitions方法：

protected void doRegisterBeanDefinitions(Element root) {
	
		BeanDefinitionParserDelegate parent = this.delegate;
		this.delegate = createDelegate(getReaderContext(), root, parent);

		if (this.delegate.isDefaultNamespace(root)) {
			String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
			if (StringUtils.hasText(profileSpec)) {
				String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
						profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
				if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
					if (logger.isInfoEnabled()) {
						logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
								"] not matching: " + getReaderContext().getResource());
					}
					return;
				}
			}
		}

		preProcessXml(root); //这个方法是空的，受protected修饰，供子类继承覆盖，模板方法模式
		parseBeanDefinitions(root, this.delegate);
		postProcessXml(root); //这个方法是空的，受protected修饰，供子类继承覆盖，模板方法模式

		this.delegate = parent;
	}

继续追踪到parseBeanDefinitions方法：

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		if (delegate.isDefaultNamespace(root)) {
			NodeList nl = root.getChildNodes();
			for (int i = 0; i < nl.getLength(); i++) {
				Node node = nl.item(i);
				if (node instanceof Element) {
					Element ele = (Element) node;
					if (delegate.isDefaultNamespace(ele)) {
						parseDefaultElement(ele, delegate);//默认标签的解析
					}
					else {
						delegate.parseCustomElement(ele);//自定义标签的解析
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}